1. Field of the Invention
The present invention relates to rectangular RF anechoic chamber technology and more particularly, to an improved design of rectangular RF anechoic chamber where the material or absorbing material attached to its feeding wall has a homogeneous property on X-Y plane, i.e. the plane parallel to the feeding wall. And the measurement antenna(s) are mounted on the feeding wall from which the material with a homogeneous property will reduce interferences from the fields which produce scattered fields from the wall; and may produce a quiet zone with significantly improved quality, and specially at low frequency band. The quiet zone quality described herein means the field uniformity in the test zone, or the magnitude of ripple of the field strength in the test zone.
2. Description of the Related Art
When testing the radiation pattern and radiation efficiency of an antenna, the radiation power and receiving sensitivity of a wireless apparatus or the RF spurious emission of a device in a RF anechoic chamber, the quality of the quiet zone affects the measurement accuracy directly.
A conventional rectangular RF anechoic chamber 10, as shown in FIG. 1 and FIG. 1A, generally has a pyramidal absorber 13 attached to its feeding wall 12, and one or a number of measurement antennas 14 installed on its feeding wall 12 (see FIG. 1A) or kept at a distance from its feeding wall 12 (see FIG. 1). According to this design, it is difficult to get a high quality quiet zone 15 at low frequencies, for example, below 700 MHz. In order to produce a high quality quiet zone 15 at low frequency band, it is necessary to use a larger size RF anechoic chamber 10 with a larger absorbing materials and to have the electromagnetic fields of MA(s) illuminating the absorbing materials in a smaller off-normal incident angles. When making tests at low frequencies, or selecting an alternative option, a tapered RF anechoic chamber is usually used for the sake of having a better low frequency quiet zone 15. However, a rectangular RF anechoic chamber is easier to construct than a tapered RF anechoic chamber, more particularly under the requirement for a high shielding effectiveness test environment.
Following increasing in low-frequency band applications, such as digital video broadcasting (DVB), very high frequency (VHF) communications and radio-frequency identification (RFID) technology, 4G LTE communications, it is desirable to provide an improved structure of rectangular RF anechoic chamber that improves the measurement accuracy at low frequencies and reduces the cost.